Method and apparatus for treating filler-containing material such as recycled fibers

ABSTRACT

A method and apparatus for treatment of recycled fiber material and/or of the reject fraction discharged from paper mill screening systems of the short circulation of a paper machine, recover fillers as completely as possible and return the fillers back to the process as efficiently and economically as possible. The loss of fiber/mineral discharge as mill rejects from vortex cleaning and filler manufacture is decreased by treating a concentrated mineral fraction of the rejects to disperse the filler-mineral fraction and return the filler back to the paper making process.

CROSS REFERENCE TO RELATED APPLICATION

This application is a U.S. national phase of PCT/FI95/0711.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a method and apparatus in the treatmentof the fiber fraction exiting from treatment of recycled fibers, and/orfrom vortex cleaning of a paper mill as mill reject, and/or in general afraction exiting as a mineral-containing reject. As known, sources ofrecycled fibers include, for example, so-called broke of a papermachine, which may be recycled as raw material, and the actualpost-consumer waste paper and board. The present invention especiallyrelates to the treatment of recycled fiber materials of this kind insuch a way that the fillers contained in the materials may be recoveredas completely as possible and returned to the process as efficiently andeconomically as possible.

In the short circulation of paper machines manufacturingfiller-containing paper grades and especially coated paper grades, asubstantial amount of mineral and pigment fraction is dischargednowadays from the process as mill reject of a vortex cleaning plantwhich as a material could be utilized as raw material for paper but theparticle size of this material is too coarse. Another source ofmineral-containing rejects in a paper mill are filler and coatingpigment manufacturing processes and the flushing waters from theapparatus used in these processes.

In the short circulation of paper machines manufacturing SC grades andother filler-containing grades, the mineral fraction exiting the vortexcleaning as mill reject is the coarse portion of the mineral fraction,i.e. the filler, supplied in the pulp dosing and usually having aparticle size of over 10 μm.

In the short circulation of paper machines manufacturing coated papergrades, the mineral fraction exiting the process as mill reject mainlycontains non-dispersible coating layer of coated broke. The coatinglayer has not dispersed in the broke dispersion system to particles fineenough. This fraction of the coating layer, usually having a particlesize of over 10 μm, is rejected in the vortex cleaning of the shortcirculation.

The same applies also to systems for recycled pulp, in which coatedmagazine paper or like heavily coated raw material for recycled paper isused as the raw material. In the defiberizing system for recycled pulpthe coating layer of the coated paper is detached from the fiber layerof the paper itself more of less in sheet-like fractions, which becomepartially crumbled in the process. The crumbling and dispersion are,however, not complete and thus, these non-dispersed coating pigmentparticles are discharged from the process as reject of the vortexcleaning in the screening stage of the recycled pulp line. However, inview of their raw material composition, a major part of these particleswould be usable in the paper manufacture as filler which may have to beadded to the pulp suspension at a later stage in the paper manufacture.The size of these particles, however, will cause problems in the papermachine itself if the particles are not dispersed and thus made usableas filler.

In an arrangement according to the invention, the filler/mineral lossexiting as mill reject from the vortex cleaning process and/or as rejectfrom the manufacture of filler or coating pigment is reduced by treatingthe fraction having a concentrated mineral content in the vortexcleaning plant in order to disperse the mineral fraction and to returnit to the process.

The method and the apparatus of the present invention provide forexample the following advantages:

Filler/mineral, water, chemical, heat and fiber losses as small aspossible. Only the useless fraction and the fraction that cannot beprocessed into a usable form are discharged in a highly concentratedform.

Dispersion of mineral particles is based on internal shear forces of thesuspension; in other words mechanical wear is minimal.

Investment costs of the system are very low. The invention istechnically carried out with commercial apparatus, repayment period isshort.

System is easy to build, i.e. it may also be established in existingsystems by collecting mineral-containing rejects from various sourcesand by adding in the process, for example, subsequent to the lastcleaner step or inside the cleaner plant, a screen to fractionate themineral fraction and the organic fraction, and a cleaner of a new typefrom which the rejected flow is discharged in a highly concentratedform, and by adding in the process after these stages a treatment stagefor dispersing the mineral fraction.

The treatment is preferably carried out in the short circulation of apaper machine for each machine individually; thus for example the watercirculations of the machines are not mixed.

The system is a continuously operating part of a short circulation of apaper machine, or of a screening system. In other words, the processconditions are constant and the operation trouble-free.

The process adjusts itself, for example, if the amount of coarsefraction increases, the system returns only the dispersed fraction tothe process and the rest is discharged from the system.

The characteristic features of the method and the apparatus of theinvention become apparent in the enclosed patent claims.

The method and the apparatus of the present invention are described morein detail below, by way of example, with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a and 1b schematically illustrate two prior art filler recoverysystems;

FIG. 2 schematically illustrates an other prior art filler recoverysystem;

FIG. 3 illustrates yet another prior art filler recovery system;

FIGS. 4a-4c illustrate 100 times enlarged photographs of the materialfed to the curved screen of the apparatus of FIG. 2 and both fractionsobtained from the curved screen;

FIG. 5 illustrates a few preferred embodiments of the invention combinedin one and the same figure;

FIG. 6 illustrates another preferred embodiment of the invention; and

FIG. 7 illustrates yet another preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

An example of a prior art arrangements for diminishing filler/minerallosses is, for example, the arrangement illustrated in FIG. 1a. Therethe mineral loss is diminished by fractionating fine material havingparticle size smaller than the slots of the curved screen, i.e. theuseful solids, from the discharge flow of the process back to theprocess. The apparatus operates in such a way that the flow dischargedfrom the process is brought to a curved screen 10, a so-calledHydra-Screen, which divides the flow into two fractions. The coarserfraction is led to an intermediate tank 12 and the finer fraction to afiltrate tank 14. The finer fraction is pumped from the filtrate tank 14by a pump 16 to a curved screen 18, a so-called Micra-Screen, of thesecondary stage, the coarser fraction of which is led to theintermediate tank 12 and the finer fraction, practically speaking allthe liquid and the filler flowing with it, is recycled to be reused inthe process for example in dilution. The fraction discharged from theintermediate tank 12 as reject of the curved screens 10 and 18 is pumpedby a pump 20, for example, to a filter press 22, for thickening thecoarse fraction to a more easily treatable consistency. Besides thecurved screen 10 illustrated in FIG. 1a, a finely perforated/slottedpressure screen or vortex cleaners (FIG. 1b), such as so-called trapcleaners commonly used in sand separation, may be used as afractionation apparatus.

As illustrated in FIG. 1b, the material to be treated is obtained asreject from the third or fourth step of a vortex cleaning plant 32, andthis rejected fine fraction is recycled for reuse. The material rejectedfrom the vortex cleaning plant is brought by a pump 34 to a curvedscreen 36, which preferably is a so-called Micra-Screen, and the liquidaccepted by this curved screen, the so-called filtrate, is led to a wirepit or, for example, to be used for dilution in a secondary screeningapparatus. The reject of the curved screen 36, in other words thethicker fraction, on the other hand is led to the suction side of a pump38 and therefrom it is pumped further to a cleaner 39, which preferablyis a so-called Eliminator-cleaner, which is disclosed, for example, inU.S. Pat. No. 5,139,652. The accept from the cleaner 39 is led to thesuction side of a feed pump 30 of the third or fourth step 32 of thevortex cleaning plant to be pumped for recirculation.

However, it is characteristic of all the above methods that they do notchange/diminish the particle size/distribution of the solids to berecovered but only separate the finest and as such at least partlyusable fraction and the coarse fraction and return the fine fraction touse.

It is a characteristic feature of a dispersion process of mineralfractions according to the invention that it is based on mechanicallygenerated internal shear forces of the flow/suspension. To have shearforces which have a dispersing effect, i.e., enough efficiency, theconcentration of the suspension has to be high. The principle is thatthe higher the concentration is in which the treatment is carried outthe more efficient it is; or, the higher shear forces may be directed tothe suspension and the more efficiently the dispersion takes place.

The concentration of the mineral fractions is in a practical wayincreased by means of a new kind of vortex cleaner constructiondisclosed in U.S. Pat. No. 5,139,652, said cleaner being extremelyefficient in classifying but from which the coarse mineral fraction,having a size of over 10 μm, is rejected as a highly concentrated flowhaving a solids content of even more than 40%.

The concentration of the fraction to be treated may be increased also,for example, by filtering or precipitating, but it is characteristic ofall these other methods that they require additional apparatus and/orlarge volumes and time and are very complicated to use as a continuous,trouble-free process. The concentration of the mineral fraction in thenew kind of vortex cleaner takes place in connection with the normaloperation of the vortex cleaner without any additional apparatus.

After the thickening, i.e. the increase of the solids concentration, themineral fraction is treated by mechanical mixing elements or grindingapparatus generating great internal shear forces in the suspension. Dueto the shear forces the mineral particles rub against each other and arecomminuted to such a particle size that they may be used as a filler inpaper manufacture.

The embodiment illustrated in FIG. 2 is based on the process describedin Finnish patent no. 93753. The patent describes a method of treating afiller-containing material such as recycled fiber. According to themethod, the recycled fiber material is treated in a multi-step vortexcleaning plant, in the last step of which the material is divided intotwo fractions the finer of which is returned to use and the coarserfraction, i.e. the reject is forwarded to further processing. It ischaracteristic of the method of the patent that the reject is suppliedto a first fractionation stage, divided into two fractions the finerfraction of which is returned to the vortex cleaning plant and thecoarse fraction is taken to a refining stage, it is refined and therefined material is taken to the last fractionating stage in which thecomminuted material is divided into two fractions of which the finefraction is returned to the process. Thus, according to the method, thereject from the vortex cleaning plant is fractionated so that the finematerial is returned to the vortex cleaning plant and the coarsefraction is further treated.

FIGS. 2 and 3 illustrate an alternative of the method disclosed in theFinnish patent no. 93753 which are also disclosed in WO patentapplication no. PCT/FI94/00086. In FIG. 2, the coarse reject, which mayhave an ash content as high as 60-90%, from the last vortex cleaningstep 32 is transported by means of a pump 80 and diluted withcirculation water preferably containing as little solids as possible,for example with the clear filtrate S from fiber recovery, to the feedof a curved screen 82, for example a so-called Micra-Screen. The screensurface of the curved screen 82 may have a slot size of for example100-250 μm. The curved screen divides the feed flow into a thickerfraction and a filtrate. All coarse fractions containing fiber, shives,and impurities are removed in the thicker fraction. Mineral particlesthat have passed through the slots of the said 100-250 μm size, and mostof the water constitute the filtrate. The filtrate from the curvedscreen 82 is transported, by means of a pump 84 and diluted preferablywith circulation water S containing as little solids as possible, to thefeed of vortex cleaners 86. The accept from the vortex cleaners 86 whichcontains the majority of the water and the fine filler fraction of asize smaller that 10 μm, is returned for example to the feed of the lastvortex cleaner to a pump 88, to the broke system, screening of broke orthickening of broke as illustrated by broken line B. The reject from thevortex cleaner step 86 contains the mineral fraction exceeding theparticle size of 10 μm in a highly concentrated state of approx. 30-50%dry solids content. The reject is guided, for example, by means of freefall to a dispersion apparatus 90 in which the mineral particles in thereject are subjected to strong shear forces. The mineral particles arecomminuted and most of the flow leaving the dispersion apparatus 90 hasa homogenous particle size and is usable filler fraction of a size lessthan 10 μm.

The mineral fraction comminuted in the dispersion apparatus 90 isreturned by means of the pump 84 to the feed of the vortex cleaning step86 operating the in the way described above. Thus, a non-dispersedmineral fraction may be circulated in the dispersion apparatus 90 andthe vortex cleaners 86 until the mineral particles have been dispersedto a size suitable for use as filler.

FIG. 3 illustrates an alternative to FIG. 2. The only significantdifference when compared to FIG. 2 is that a pressure screen 92 has beenused instead of a curved screen, the pressure screen dividing, like thecurved screen, the reject from the vortex cleaning process 32 and/or themineral-containing reject to a coarse fraction to be removed from theprocess and to a fraction containing mineral particles and to be furthertreated; the treatment has already been described in connection withFIG. 2. The pressure screen preferably employs a screen drum with a verysmall perforation (aperture diameter 0.15-0.20 mm). Further, it shouldbe noted that the use of a pressure screen 92 makes the use of the pump84 illustrated in FIG. 2 unnecessary as the fine fraction obtained fromthe pressure screen may in a pressurized state be supplied directly tothe vortex cleaners 86. Another difference in the embodiment of FIG. 3as compared with the embodiment of FIG. 2 is that the material dispersedin the dispersion apparatus 90 is returned to the feed of the pressurescreen 92 and not directly to the vortex cleaners as in FIG. 2.

Of course, also in the embodiments illustrated in FIGS. 2 and 3, it ispossible to arrange several subsequent dividing and dispersing stages,for example, as illustrated in FIG. 4 of the Finnish patent mentionedearlier. Further, it is also possible to convey the dispersed materialfrom the dispersion apparatus 90, for example, to another dividing stage94 (the entire process part has been illustrated with broken linesbecause of its optional character), from which the usable fine materialis returned to use and the coarse fraction is rejected and dischargedfrom the system.

The FIG. series 4a-4c illustrates the feed of the curved screen (FIG.4a), the filtrate (FIG. 4b) and the reject or the thicker fraction (FIG.4c) of the process according to FIG. 2. The figures clearly show how allthe fiber-containing fraction and the large mineral particles of thefeed in FIG. 4a have been rejected to the thicker fraction of FIG. 4c,while the filtrate, FIG. 4b, contains only mineral fraction.

FIG. 5 illustrates a version developed further from the process of FIGS.2 and 3. This version on one hand concentrates on treating the coarsefraction, i.e. the thickened fraction, from the curved screen 82 of FIG.2 or correspondingly from the pressure screen 92 of FIG. 3. On the otherhand, FIG. 5 illustrates a new way of treating and recycling amineral-containing fraction. In FIG. 5, the coarse reject having an ashcontent of as high as 60-90%, is transported, by means of pump 80 anddiluted for example with the clear filtrate S obtained from fiberrecovery and preferably containing as little solids as possible, to thefeed of a screen apparatus 102, for example a curved screen, a so-calledMicra-Screen (illustrated in the figure), or of a pressure screen, aso-called Ahldecker. When a curved screen is employed the screen surfacehas slot size of for example 100-250 μm. When a pressure screen is used,it preferably is a perforated drum having an aperture diameter ofapprox. 0.15-0.20 mm. The inlet flow of the screen apparatus 102 isdivided into a thicker fraction and filtrate. All coarse fractionscontaining fibers, shives, and other impurities are removed from thethicker fraction. Mineral particles that have been able to pass throughthe slots of the said 100-250 μm and most of the water end up in thefiltrate. From the screen apparatus 102 the filtrate, which is diluted,preferably with circulation water S containing as little solids aspossible, is transported by means of a pump 104 to the inlet flow ofvortex cleaners 106. If the screening apparatus 102 is a pressurescreen, pump 104 is not necessary. The accept from the vortex cleaners106 containing the most part of the water and the fine filler fractionof less than 10 μm is returned for reuse for example via broke treatmentor wire pit. The reject from the vortex cleaning step 106 contains themineral fraction of the size over 10 μm in a high solids concentrationof approx. 30-50%. This reject is taken for example by free fall to agrinding means 110, which may be a dispersion apparatus or a grinderdeveloped specially for this purpose and in which the solid materialparticles in the reject are subjected to intensive shear forces. Themineral particles are broken down and most of the flow discharged fromthe grinding means 110 is usable mineral fraction of homogenous particlesize of less than 10 μm.

According to a preferred embodiment of the invention, part of themineral fraction refined in the grinding means 110 is returned by a pump104 to the inlet of the vortex cleaning step 106 operating in the waydescribed above. (Another way has been described in connection with FIG.2 according to which the whole refined fraction is returned to thevortex cleaning step.) Part of the refined mineral fraction is returnedwith the thickened fraction from the screen apparatus 102 to furthertreatment. Thus, the non-refined mineral fraction may be recirculated inthe grinding means 110 and the vortex cleaners 106 until the mineralparticles have broken down to a size usable as a filler.

In previous embodiments, at least in the ones illustrated in FIGS. 2 and3, the focus has not been on the treatment of the thickened frictionobtained from the screen apparatus. In a preferred embodiment of theinvention the thickened fraction from the screen apparatus 102 is takento an intermediate tank 112 into which also dilution liquid D issupplied; the liquid may be for example clear filtrate from fiberrecovery. The thickened fraction from the screen apparatus 102 isdiluted in the intermediate tank 112 provided with a mixer 114 to ensurehomogenous consistency. The diluted fraction is forwarded by a pump 116to vortex cleaners 118 which separate the usable fiber and the finefiller fraction which are recycled to use via, for example, the broketreatment system. The reject from the vortex cleaners 118 which containsamong other things large fiber lumps, impurities and mineral pieces, istaken according to a preferred embodiment of the invention to a screwthickener 120 which increases the consistency of the reject as high aspossible, and thus the reject at the discharge consistency of the screwthickener 120 may be transported directly for instance to combustion. Ifdesired, for avoiding liquid effluent, the filtrate from the screwthickener 120 is returned, for example, to the intermediate tank 112;thereby also the fines contained in the filtrate are recovered. Anotheralternative (indicated in FIG. 5 by a broken line) is to return thefiltrate from the screw thickener to the inlet flow of pump 80 wherebythe mineral particles in the filtrate may be accepted at the curvedscreen 102 and be transported further to dispersion.

As already stated above, part of the material refined by the grindingmeans 110 may be returned with the reject from the screen apparatus 102for further treatment. This is most practically done by guiding thefines fraction to the intermediate tank 112 and mixing it there with thereject from the screen apparatus 102 whereby the fine fraction which hasbeen adequately refined is accepted in the vortex cleaners 118 and isreturned that way to use.

FIG. 6 illustrates yet another preferred embodiment of the inventioncombined with the process illustrated in FIG. 5, although the partialprocess described in the embodiment does not presuppose employing allthe other partial processes of FIG. 6. This embodiment is based on theidea which we have found out in tests we have performed that dispersionmay be intensified both by treating the fraction to be dispersed withchemicals and by heating it. Naturally it is possible to treat thefraction at the same time both with chemicals and by heating and eitherprior to or during the dispersion. The heating is preferably done withsteam. In the embodiment of FIG. 6, chemicals and/or steam is added tothe fraction obtained as reject from the vortex cleaner 106 for exampleby injecting at 130 prior to the dispersion apparatus or prior to avertical pipe 108.

When heating the fraction to be dispersed, attention should be paid tothe fact that the fraction may contain stickies, glues, binding agents,plastics-based substances, etc. which should not be allowed to soften somuch that they stick to the process piping or process equipment. Also,one should be very careful when using the chemicals employed to softenthe mineral fraction, the so-called latex softeners; they must notpromote adhering of the stickies.

This embodiment provides among other things the advantage that itimproves efficiency because the dispersion is directed only to thefraction requiring dispersion.

FIG. 7 illustrates yet another preferred embodiment of the invention. Infact, the process is of the same types as illustrated in FIG. 6,employing an intermediate tank 79, 115 and 103 prior to a pump 80, 116and 104'. The intermediate tanks may be of the same type as theintermediate tank 112 illustrated in FIG. 6, i.e. tanks provided with amixer to ensure that the mineral fraction is not sedimented on thebottom of the tank and to ensure that the mineral concentration of theliquid to be pumped further is practically stable. The tanks 79, 115 and103 may be of the same type, also, as the tank 18 in FIG. 6, i.e. havinga fairly small diameter and preferably such a form that the mineralfraction cannot easily concentrate. Further, the supply of dilutionliquid to the intermediate tanks 79, 115, and 103 has preferably beenarranged so that the flow of the dilution liquid causes the content ofthe intermediate tank to rotate, which prevents the mineral particlesfrom settling. The mixing, itself, of the liquid and the mineralparticles to form a homogenous suspension takes place in the pumpsfollowing the intermediate tanks.

As can be understood from the many embodiments of the inventiondescribed above which to some extent differ from each other, a newmethod and apparatus previously not known has been developed fortreating recycled fiber material so that as much as possible of theminerals and usable fiber therein can be recovered fore reuse. Firstly,it must be noted that all the apparatus described and illustrated in theFigs. have been connected to each other via flow paths suitable for thatpurpose and either illustrated in the figures, described in thedescription or mentioned in the claims. It must also be noted that thescreening and fractionating devices mentioned above, i.e. vortexcleaners, pressure screens, and curved screens are interchangeable whereappropriate and that they may be replaced by other devices performingthe same task. In other words, in the embodiments of the presentinvention described above, the treatment the devices carry out iscritical, not the type of the device. Further, it should be noted thatthe embodiments presented above are examples, only, of the manyvariations of the invention and they do not by any means intent to limitthe invention to the embodiments described. It should also be understoodthat although a vortex cleaning plant has been discussed above, thereject of which is treated with the process of the present invention,the type of the cleaning plant is not important in view of the inventionbut the reject of the plant. This means that it does not matter how thewood-based fiber material and mineral particles have been separated to aseparate fractions, they may in any case be further treated by theprocess of the invention. Thus, it is clear that although a grinder or amill type refiner has been described above as the mixing/grindingdevice, also a tank provided with one or several mixing/refining rotorsmay be used as the refining apparatus. It is also clear that the variousdetails described in connection with different embodiments may beemployed also in other embodiments where applicable, although that hasnot been specifically mentioned. Further, it should be remembered thatthe use of steam and/or chemicals prior to dispersion, described in theembodiment of FIG. 6, may alone be employed in all possible dispersionapplications without the other partial processes illustrated in FIG. 6.Thus, the invention is defined by the appended patent claims, only.

I claim:
 1. Apparatus for treating mineral containing recycled fibersfrom a paper mill, comprising:a vortex cleaning plant for separatingrecycled fibers into an accept fraction and a reject fraction; means forfractionating rejects associated with the vortex cleaning plant, andother mineral-containing rejects from the paper mill, in a firstfractionating stage to produce a second accept fraction and a secondreject fraction; mixing and dispersing means for treating said secondaccepts fraction; and means for treating said second reject fraction torecover fillers therefrom, including a screening stage to divide thesecond reject fraction into a filler fraction which is reused, and acoarse mineral fraction.
 2. Apparatus as recited in claim 1 wherein saidfirst fractionating stage comprises screening means.
 3. Apparatus asrecited in claim 2 wherein said screening means comprises at least onecyclone separator.
 4. Apparatus as recited in claim 2 further comprisinga screw thickener for thickening said second rejects from said screeningmeans.
 5. Apparatus as recited in claim 1 further comprising a screwthickener for thickening said second rejects from said firstfractionating stage.
 6. Apparatus as recited in claim 1 wherein saidfirst fractionating stage comprises a pressure screen.
 7. Apparatus asrecited in claim 1 wherein said screening stage comprises at least onecyclone separator.
 8. Apparatus as recited in claim 1 wherein saidscreening stage comprises a pressure screen.
 9. A method of treating atleast recycled fibers including minerals from a paper making process,comprising:(a) vortex cleaning the recycled fibers to divide them into afirst, finer, fraction and a second, coarser, fraction; (b) using thefirst, finer, fraction in the paper making process; (c) treating thesecond, coarser, fraction in a first dividing stage by dividing it intothird and fourth fractions, the third fraction primarily comprisingshives and like wood-based materials and impurities, and the fourthfraction comprising primarily minerals; (d) treating the third fractionto recover useful fiber material therefrom; and (e) further treating thefourth, primarily mineral, fraction to produce usable minerals, andreturning the usable minerals to the paper making process.
 10. A methodas recited in claim 9 wherein (e) is practiced in a second screeningstage which divides the fourth fraction into a reusable filler fraction,and a coarse mineral fraction.
 11. A method as recited in claim 10further comprising dispersing the coarse mineral fraction, and returningat least a portion of the dispersed coarse mineral fraction to thesecond screening stage.
 12. A method as recited in claim 11 furthercomprising further treating at least a portion of the dispersed coarsemineral fraction.
 13. A method as recited in claim 12 wherein furthertreating of the dispersed coarse mineral fraction from (c), and thethird fraction in (d), are practiced by dilution and then screening. 14.A method as recited in claim 9 wherein (e) is practiced by dispersingand diluting the fourth fraction, and effecting at least one of heatingand treating with chemicals of the fourth fraction while it is dilutedso as to produce a usable mineral fraction.
 15. A method as recited inclaim 14 wherein (e) is further practiced by adding at least one ofsteam and chemicals to the fourth fraction prior to dispersion.
 16. Amethod as recited in claim 9 wherein (c) is also practiced using othermineral-containing rejects from the paper making process.
 17. A methodas recited in claim 9 wherein (d) is practiced in a screening stage,from where usable fiber material is returned back to the process.
 18. Amethod as recited in claim 17 comprising the further step of dilutingthe third fraction before said screening stage.
 19. A method of treatingat least recycled fibers including minerals from a paper making process,comprising:(a) vortex cleaning the recycled fibers to divide them into afirst, finer, fraction and a second, coarser, fraction; (b) using thefirst, finer, fraction in the paper making process; (c) treating thesecond, coarser, fraction in a first dividing stage by dividing it intothird and fourth fractions, the third fraction primarily comprisingshives and like wood-based materials and impurities, and the fourthfraction comprising primarily minerals; and (d) further treating thefourth, primarily mineral, fraction to produce usable minerals, andreturning the usable minerals to the paper making process by dispersingand diluting the fourth fraction, and effecting at least one of heatingand treating with chemicals of the fourth fraction while it is dilutedso as to produce a usable mineral fraction.
 20. A method as recited inclaim 19 wherein (d) is further practiced by adding at least one ofsteam and chemicals to the fourth fraction prior to dispersion.